These familar round galls on the stems of goldenrods are made by the goldenrod gall fly (see: http://www.pbase.com/fwg/image/104072334). Inside these galls, a fat grub waits for spring, but many never make it out of these galls because various species of wildlife feed on them. You'll often see downy woodpeckers, for example, pecking away at the galls to extract the larva inside.